1. Field of the Invention
The present invention relates to an actuator for use in controlling a stylus attached to the end of a pickup arm of a video disk player and other uses, and, more particularly, to an actuator of movable magnet type.
2. Description of the Prior Art
The video disk system can be broadly sorted into two types: namely a contact read out type system represented by an electrostatic system and a noncontact read out type system represented by an optical system.
The most popular system of contact read out type incorporates a disk having a tracking groove along which a stylus is fed, and the signal is detected as a change in the capacitance between the contacting surface of the stylus and the disc surface. A pickup device for a video disk player used in combination with the video disk having tracking grooves comprises a pickup means including cantilever, a stylus tip provided at one end of the cantilever (which is called a "readout end"), a thin conductive electrode tip attached to the stylus tip and a magnetic disk plate attached to the other end of the cantilever, and an actuator which is disposed adjacent to the magnetic disk plate magnetically coupled thereto for actuating the cantilever to compensate the stylus position in a jitter direction. Although the surface of the groove in the disc is smooth macroscopically, this surface has a number of microscopic convexities and concavities so that the relative velocity between the disc and the stylus is changed undesirably in the direction of the jitter. To compensate for this change, an error signal is applied to the actuator to move the cantilever in the direction of the jitter.
An example of this kind of actuator is shown in FIG. 2 of the Japanese patent application Laid-open No. 4154/1974. This actuator has a stationary yoke in which are fixed pole shoes and a permanent magnet, and a solenoid coil is disposed in the magnetic gap of the yoke. The solenoid coil itself is moved back and forth as it is selectively energized. This type of actuator is generally referred to as "moving coil type actuator" and is finding wide use. The moving coil type actuator, however, has an extremely low efficiency of transformation of energy. In addition, it is difficult to obtain a sufficiently high reliability of the construction of the electric power feeder for feeding the electric power to the movable solenoid coil.